The purpose of the proposed research program is to define the molecular structure, genetic organization and regulatory function of the Drosophila Y chromosome during spermatogenesis. Initial studies will be directed toward the development of a method of Y chromosome isolation; subsequent characterization of Y chromosomal DNA sequences will be accomplished by DNA/DNA hybridization techniques and the utilization of bacterial restriction endonucleases and will probably include the formation and selection of hybrid recombinant DNA molecules between the Drosophila Y chromosome and plasmids of E. coli. Genetic analysis will utilize the detection and recovery of temperatue-sensitive male sterile mutations which will then be subjected to cytogenetic analysis as a measure of Y chromosomal activity during spermatogenesis. Biochemical assay of spermiogenesis will qualitatively and quantitatively describe testicular macromolecular (RNA, protein) biosynthesis in vitro.